Added config option. (#1324)

* feat: Added config option.

src/cli.rs

@@ -55,6 +55,23 @@ A feature name may not contain whitespace. You can activate multiple features:
 
 If more than one feature sets the same option, the last one wins.
 
+If an option is present in the [delta] section, then features are not considered at all.
+
+If you want an option to be fully overridable by a feature and also have a non default value when
+no features are used, then you need to define a \"default\" feature and include it in the main
+delta configuration.
+
+For instance:
+
+[delta]
+feature = default-feature
+
+[delta \"default-feature\"]
+width = 123
+
+At this point, you can override features set in the command line or in the environment variables
+and the \"last one wins\" rules will apply as expected.
+
 STYLES
 ------
 
@@ -276,6 +293,10 @@ pub struct Opt {
     /// intended for other tools that use delta.
     pub color_only: bool,
 
+    #[arg(long = "config", default_value = "", value_name = "PATH")]
+    /// Load the config file at PATH instead of ~/.gitconfig.
+    pub config: String,
+
     #[arg(
         long = "commit-decoration-style",
         default_value = "",
@@ -1135,7 +1156,16 @@ impl Opt {
         git_config: Option<GitConfig>,
         assets: HighlightingAssets,
     ) -> Self {
-        Self::from_clap_and_git_config(env, Self::command().get_matches(), git_config, assets)
+        let mut final_config = git_config;
+        let matches = Self::command().get_matches();
+
+        if let Some(path) = matches.get_one::<String>("config") {
+            if !path.is_empty() {
+                final_config = Some(GitConfig::try_create_from_path(&env, path));
+            }
+        }
+
+        Self::from_clap_and_git_config(env, matches, final_config, assets)
     }
 
     pub fn from_iter_and_git_config<I>(

src/git_config/mod.rs

@@ -5,7 +5,6 @@ pub use git_config_entry::{GitConfigEntry, GitRemoteRepo};
 use crate::env::DeltaEnv;
 use regex::Regex;
 use std::collections::HashMap;
-#[cfg(test)]
 use std::path::Path;
 use std::str::FromStr;
 
@@ -65,11 +64,41 @@ impl GitConfig {
         }
     }
 
+    #[cfg(not(test))]
+    pub fn try_create_from_path(env: &DeltaEnv, path: &String) -> Self {
+        use crate::fatal;
+
+        let config = git2::Config::open(Path::new(path));
+
+        match config {
+            Ok(mut config) => {
+                let config = config.snapshot().unwrap_or_else(|err| {
+                    fatal(format!("Failed to read git config: {err}"));
+                });
+
+                Self {
+                    config,
+                    config_from_env_var: parse_config_from_env_var(env),
+                    repo: None,
+                    enabled: true,
+                }
+            }
+            Err(e) => {
+                fatal(format!("Failed to read git config: {}", e.message()));
+            }
+        }
+    }
+
     #[cfg(test)]
     pub fn try_create(_env: &DeltaEnv) -> Option<Self> {
         unreachable!("GitConfig::try_create() is not available when testing");
     }
 
+    #[cfg(test)]
+    pub fn try_create_from_path(_env: &DeltaEnv, _path: &String) -> Self {
+        unreachable!("GitConfig::try_create_from_path() is not available when testing");
+    }
+
     #[cfg(test)]
     pub fn from_path(env: &DeltaEnv, path: &Path, honor_env_var: bool) -> Self {
         Self {

src/options/get.rs

@@ -9,7 +9,7 @@ use ProvenancedOptionValue::*;
 // Look up a value of type `T` associated with `option name`. The search rules are:
 //
 // 1. If there is a value associated with `option_name` in the main [delta] git config
-//    section, then stop searching and return that value.
+//    section, then stop searching and return that value (steps 2 and 3 are not executed at all).
 //
 // 2. For each feature in the ordered list of enabled features:
 //

src/options/set.rs

@@ -135,6 +135,7 @@ pub fn set_options(
             blame_timestamp_format,
             blame_timestamp_output_format,
             color_only,
+            config,
             commit_decoration_style,
             commit_regex,
             commit_style,